The present invention relates to a novel and advantageous process for cleaning substrates, in particular masks and mask blanks. In a transverse sectional view of the intermediate portion, the first direction and the second direction are directions directed towards a first side of the intermediate portion. In the invention the plurality of channel IF units and the plurality of disk IF units are connected via a selector to the cache memory unit whereas the plurality of channel IF units and the plurality of disk IF units are directly connected to the shared memory unit with no selectors. Thus, it becomes possible to determine whether the amount of toner consumption is correctly updated based on the request flag and accurately monitor the amount of toner consumption.